It is known in the art to form fertilizer materials into the form of a stake or peg which is driven into the ground around a plant or tree to provide the necessary fertilizer each time it rains. Such stakes or pegs are formed of the pure fertilizer compositions and have no sustained release characteristics. Water-soluble nutrients applied in this manner or mixed with the soil provide an abundance of nutrients initially but are followed by progressively poorer results as the growing season progresses. This is especially apparent with blue grass which produce abundant first crops and poorer second and third crops when so treated. Much of the water-soluble nutrients is wasted by leaching during rains and watering.
Water-insoluble slow acting fertilizers, such as a urea-formaldehyde reaction product, which is relatively expensive form of nitrogen, seldom provide for the desired growth of the plants initially or for sustained growth over a normal growing season, because the fertilizer is not released in accordance with plant needs. Those essential nutrients as nitrogen and phosphorus are fixed and as a result considerable amounts of them never become available for plant growth.
The art has appreciated the desirability of controlled release of fertilizers for a long time, as shown by Ellis U.S. Pat. No. 847,749, dated 1907. A wide variety of coatings and porous films have been suggested for this purpose. These means have proven to be impractical because they release the fertilizer too rapidly or too slowly, or release all of the fertilizer at once or fail to release any of the fertilizer. Wax coatings have a tendency to burst and the particles have a tendency to agglomerate. Films on the other hand are not of uniform porosity, thus making controlled release impossible.
Work done for the Wisconsin Alumni Research Foundation by W. C. Dahnke, O. J. Attoe and associates reported in the Agronomy Journal, Vol. 55: 242-244 and Vol. 55: 495-499, 1963, has demonstrated that the placement of the feritilizer ammonium sulfate in perforated polyethylene bags or capsules effectively controlled the rate of release but did not significantly increase the yield or recovery of the constituents. The use of wax-coated pellets increased the recovery of nitrogen but did not affect the yield of such crops as corn. Some of these results are also reported in U.S. Pat. No. 3,059,379 as regards the perforated capsules wherein the rate of release of the fertilizer constituents is controlled by: (1) the number and size of the perforations per capsule; (2) the weight of fertilizer per capsule; (3) the solubility of the fertilizer constituents; and (4) the amount of soil moisture.